1. Field of the Invention
This invention relates to antenna structure, and, more particularly, to an antenna structure having a microstrip feed line and a smooth transition from the microstrip transmission line into a two-sided notch antenna.
2. Description of the Prior Art
In radio frequency antenna design, the objective is to provide a design which is compatible with feed networks and can be manufactured using low cost batch fabrication techniques, and at the same time provide broadband performance for impedance match and for pattern characteristics. As shown in FIG. 1, a conventional notch antenna 10 consists of a single-sided metallization 12 on a dielectric substrate 14 having the form of a flared slot. This conventional antenna 10 includes a transition from a microstrip feed line 16 to the notch antenna slot line 22, which requires slot line open circuit 20 which can only be realized in approximate form and which therefore limits the bandwidth capability of the circuit. In addition, the transition requires a through short circuit 18 in microstrip which for ceramic substrates or for millimeter wave designs can preclude low cost batch fabrication and/or may require approximate realizations which limit bandwidth performance.
Another prior art notch antenna construction is shown in U.S. Pat. No. 3,836,976 issued Sept. 17, 1974 to Monser et al and assigned to Raytheon Company. The patent disclosure includes a conventional single-sided notch antenna having a narrow region and a wide region with the transition being made in a single step. The disclosure describes a coaxial feed line which is soldered to the metallization layer, and again the transition from the feed line to the antenna creates a discontinuity which limits the bandwidth of the antenna structure.